High-density lipoproteins (HDL) or lipovitellin fraction

Abstract

HDLs are the second group of lipoproteins of yolk and account for about 1/6 of its dry matter and 36% of its proteins. They are specifically localized in granules and are designated as lipovitellin. HDLs are the result of the proteolytic cleavage of a precursor (vitellogenin), which is synthesized in the liver under the regulation of oestrogen. It can be noticed that phosvitin (see Chap. 4) comes from the same precursor. In native egg yolk, HDLs are complexed to phosvitins to form the granular structure through phosphocalcic bridges. HDLs are made up of 75-80% proteins and 20-25% lipids. So their density is close to that of proteins, 1.120 g/ml. Their lipids are composed of 65% phospholipids, 30% triglycerides, and 5% cholesterol (Cook and Martin 1969). © Springer-Verlag Berlin Heidelberg 2007.